Arabia : staging post for human migrations?

From time to time between 130 and 75 ka fully modern humans entered the Levant from Africa, which is backed up by actual fossils. But up to about 2010 most palaeoanthropologists believed that they moved no further, because of the growth of surrounding deserts, and probably did not return to the Middle East until around 45 ka. The consensus for the decisive move out of Africa to Eurasia centred on crossings of the Straits of Bab el Mandab at the entrance to the Red Sea, when sea level fell to a level that would have allowed a crossing by rafting over narrow seaways. The most likely time for such n excursion was during a brief cool/dry episode around 67 ka that coincided with an 80 m fall in global sea level: the largest since the previous glacial maximum (see Evidence for early journeys from Africa to Asia).

In 2011 finds reported from the United Arab Emirates of ‘East African-looking’ Middle Palaeolithic tools in sediment layers dated at 125, 95 and 40 ka led some to speculate that there must have been an eastward move from the Levant by anatomically modern humans (see Human migration – latest news). That view stemmed from the fact that the earliest date was during the last interglacial when sea level would have been as high as it is today, and around 95 ka it would have been little different. That report coincided with others about freshwater springs having emanated from uplifted reefs around the edges of the Arabian Peninsula during the last interglacial, and the existence of substantial lakes deep within the subcontinent around that time (see Water sources and early migration from Africa). Substantial funding followed such exciting news and results of new research are just beginning to emerge (Lawler, A. 2014. In search of Green Arabia. Science, v. 345, p. 994-999).

A team led by Michael Petraglia of the University of Oxford has used field surveys and remote sensing to reveal a great many, now-vanished lakes across the Arabian Peninsula, including many in the fearsome Rub al Khali or Empty Quarter. They are linked by an extensive, partly sand-hidden network of palaeochannels, which include several of the major wadis; a system that once drained towards the Persian Gulf. As well as abundant freshwater molluscs and other invertebrates, former lakeshore sediments are littered with huge numbers of stone tools, also with East African affinities (Scerri, E.M.L. et al. 2014. Unexpected technological heterogeneity in northern Arabia indicates complex Late Pleistocene demography at the gateway to Asia. Journal of Human Evolution, In Press http://dx.doi.org/10.1016/j.jhevol.2014.07.002). Using optically stimulated luminescence dating, which shows how long stone objects have been buried, the British team has found tools dating back as long as 211 ka, with a cluster of dates between 90 to 74 ka. Modern humans, Neanderthals and even Denisovans may have made these tools; only associated fossil remains will tell. Yet it is already clear that for lengthy periods – perhaps of a few hundred or thousand years – the hyper-arid interior of Arabia was decidedly habitable. It may have been a thriving outpost of emigrants from Africa, whose abandonment as climate shifted to extreme dryness as the last interglacial gave way to Ice Age conditions, could well have been the source of the great migration that colonised the rest of the habitable world. Petraglia’s team has already courted controversy with their claim for anatomically modern humans’ tools in South Indian volcanic ash beds that date to the Toba eruption around 74 ka: considerably earlier than the more widely accepted post-65 ka dates of human eastward migration.

2 responses to “Arabia : staging post for human migrations?”

I’ve done field work at Al Ain, though not for paleoanthropology, and I’d like to give some more information about the accompanying aerial photo of Al Ain). The crescentic cuesta running from the left foreground and curving round to the right in the middle distance, consists largely if not entirely of Oligocene carbonates and marls, including well-developed coral-and-foram rich facies, almost vertical in the foreground and becoming less steep in the distance. The massif rising up on the right consists of underlying beds of denser Eocene and (I think) Paleocene carbonates, much less rich in fossils. The whole structure, of which just a single sector is on view here is a spectacular text-book denuded pericline whose tectonic origin is related to the Late Miocene to Pliocene Zagros-Makran uplift, to the N, on the Iranian side of the Gulf.

The ancient human association is therefore not directly connected with these rocks, but rather (from the article) the Pleistocene history of the oasis and the local former river patterns, which presumably account for much of the denudation of the pericline. In fact the nearby Oman Mountainsto the E are strongly dissected by huge wadis often filled with up to 10 m or so of alluvial gravels and pebble beds. On seeing these wadis for the first time, I reflected that modern climate in the region, alone, could surely not account for such features, which must therefore be in part ‘fossil’ – and this fits with this article too.

Finally it is worth mentioning that Al Ain has a complex network of subterranean canals (Qanat / Faluj – http://en.wikipedia.org/wiki/Qanat) built to supply irrigation systems. Although very recent in terms of human history, these brilliant examples of ancient engineering are nevertheless very old in their own right, being Iron Age or older. Perhaps humans have occupied Al Ain almost continuously, from very early in their history.

Fascinating comment, Brian. I included the Al Ain spring merely as an example of an oasis in an otherwise extremely arid region – in fact in the rain shadow of the Oman mountains. Since I am in the middle of working on an educational resource about remote sensing and water exploration in arid lands, I am especially interested in the qanats that you mention so will follow that one up: Thanks for the tip. Steve Drury

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